The present invention relates to a shield tunneling method and further relates to an apparatus for assembling and disassembling form assemblies for forming a concrete lining in practicing the method.
In a typical example of conventional shield tunneling method, a steel cylindrical tube called shield is thrusted into the ground from a starting shaft to drill a hole by its front portion. A tunnel is constructed by lining the wall of a hole behind the shield during the further drilling of the hole.
The lining consists of a primary lining, using form segments, and a secondary lining made of a concrete. The primary lining is carried out by assembling arcuate segments with an erector into a ring-shaped form so that the latter is arranged circumferentially on the wall of the hole. The segments must bear long-time loading due to earth pressure and ground-water pressure and further sustain a large shield jack thrust for the shield. After the assembling of the segments, steel forms are assembled inside the segments so that a concrete lining space is defined between the segments and the steel forms. Then, a concrete is placed into the space to form the secondary lining. This concrete lining provides waterproofing and appearance finish. The steel forms are manually disassembled after setting of the concrete.
The prior art shield tunneling method is disadvantageous in the following points:
(1) The segments are costly since they must have a permanent lining structure which sustains the long-time loads in addition to the shield jack thrust and since they are buried in the concrete lining are not reused;
(2) The secondary concrete lining, which is needed for both waterproofing and finishing of the tunnel, uses a considerable part of the construction period of the tunnel and raises the construction cost; and
(3) The assembling and disassembling of steel forms, which are needed for the concrete lining, make the construction work rather laborious, thus preventing the construction period from being shortened.